Recently, the demand of radio data has been increased exponentially. In this respect, it is expected that the demand of radio data will exceed capacity that may be provided by a network based on the current cellular standard.
In order to solve this, a heterogeneous network (HetNet) based on a small cell is considered in a 3GPP LTE-A (3rd Generation Partnership Project Long Term Evolutio-Advanced) system, etc. The HetNet remarkably increases area capacity of a cell by distributing load of a macro cell and increasing a reuse rate of the macro cell as a pico cell, femto cell, a relay station and a distributed antenna system are distributed inside the macro cell depending on the situation.
Meanwhile, referring to FIG. 1, it is assumed that device-to-device (D2D) communication mutually coexists between a cellular user equipment 120, which transmits data to a base station through an uplink, and a user equipment which shares data with the cellular user equipment 120 by using the same uplink resource as that of the cellular user equipment 120. In this case, in order to assure quality of service (QoS) of the D2D communication, the cellular user equipment 120 controls intensity of interference on a D2D receiving user equipment 130 by transmitting data to a base station 110. In more detail, the cellular user equipment 120 transmits a signal by controlling a transmission power to allow intensity of interference to reach certain intensity or less. The transmission power is not greater than Pmax which is a maximum instantaneous power. Therefore, if intensity of a channel between the D2D receiving user equipment 130 and the cellular user equipment 120 is small, the cellular user equipment 120 can transmit data by increasing the transmission power. However, if intensity of the channel is great, the cellular user equipment 120 should transmit data by lowering the transmission power.
As described above, the cellular user equipment 120 transmits data such that intensity of interference on the D2D receiving user equipment 130 reaches a certain intensity or less for the following reason. The D2D receiving user equipment 130 uses a single user decoding (SUD) scheme for recovering data by regarding interference as noise when recovering its data. If the SUD scheme is used, intensity of interference is increased when the transmission power of the cellular user equipment 120 is increased, whereby performance of the D2D receiving user equipment 130 is degraded. Therefore, the cellular user equipment 120 should transmit data by lowering the transmission power to assure performance of D2D communication. As a result, loss in data transmission efficiency of the cellular user equipment 120 is caused.